The effects of acetyl-L-carnitine (ALCAR) on metabolites involved in energy and phospholipid metabolism have been evaluated by mean of 31P and 1H NMR spectroscopy on adult (6 months) and old (24 months) rat brains. A significant increase of glycerophosphorylcholin (GroPCho) in aged rat brain has been observed as compared with adult rat brain. No variations in ATP, phosphocreatine (PCr), Cr, lactate, ADP and inorganic phosphate (Pi) levels have been found between aged and adult brains. Treatment with ALCAR caused a significant increase in PCr levels and a decrease in lactate and sugar phosphate in adult and aged rat brain. These results are suggestive of treatment with ALCAR being responsible for a reduction in brain glycolytic flow and for enhancing the utilization of alternative energy sources, such as lipid substrates or ketone bodies. Furthermore, the changes in GroPCho levels observed after treatment with ALCAR may be indicative of a modulating effect on the activity of the enzymes involved in the acylation-re-acylation process of membrane phospholipids.